Weight-loss surgery might reduce cancer risk; a look at the reasons

If obesity raises the risk of cancer, it might stand to reason that weight-loss surgery could reduce the risk.

Obesity may increase the risk of death for some women with breast cancer, research finds.

Brazilian researchers are convinced – at least the ones who recently analyzed the results of 13 studies on cancer rates in the wake of weight-loss surgery. The studies, which included more than 54,000 people total, found that cancer rates among people who had undergone weight-loss surgery were about the same as cancer rates among normal weight people. Cancer rates among obese people were almost twice that.

The results were published recently in Obesity Surgery and summed up by HealthDay. The connection makes sense to Cy A. Stein, M.D., Ph.D., the Arthur & Rosalie Kaplan Chair in Medical Oncology at City of Hope and the institution's Deputy Director of Clinical Research.

“The evidence that obesity is related to an increased risk of cancer is significant, even in the modestly obese,” Stein told HealthDay. “There is an association [between obesity and cancer]. It is a risk factor for cancer development." The key word here of course is “association.” Obesity may be linked to cancer, but a link – or a correlation – is not the same as a cause. (Repeat: A correlation is not the same as a cause.) The National Cancer Institute sums up the possible connections between obesity and the increased risk for some cancers, most notably cancers of the esophagus, pancreas, colon and rectum, breast (after menopause), endometrium (or, uterine lining), kidney, thyroid and gallbladder:

"Fat tissue produces excess amounts of estrogen, high levels of which have been associated with the risk of breast, endometrial, and some other cancers.

Obese people often have increased levels of insulin and insulin-like growth factor-1 (IGF-1) in their blood (a condition known as hyperinsulinemia or insulin resistance), which may promote the development of certain tumors.

Fat cells produce hormones, called adipokines, that may stimulate or inhibit cell growth. For example, leptin, which is more abundant in obese people, seems to promote cell proliferation, whereas adiponectin, which is less abundant in obese people, may have antiproliferative effects.

Fat cells may also have direct and indirect effects on other tumor growth regulators, including mammalian target of rapamycin (mTOR) and AMP-activated protein kinase.

Obese people often have chronic low-level, or “subacute,” inflammation, which has been associated with increased cancer risk."

Stein paraphrases the science-speak up for HealthDay: “We're not sure if the obesity causes the cancer," Stein said, "but it may promote it." And that connection takes us back to a long-term prescription to reduce the risk of cancer: Exercise. City of Hope researchers were among the first to make the connection between exercise and a reduced risk of cancer. The new findings – while not conclusive on the link between weight-loss surgery and cancer risk – provide more fuel for further research. ** Learn more about City of Hope’s research on the connection between diabetes and cancer.